We've moved a site from one server to another and don't usually do any work with Drupal - all looked to be working fine on the site but the Add to Cart function is failing - it brings up a 404 error with this response

{"message":"The \u0022commerce_order\u0022 parameter was not converted for the path \u0022/cart/{commerce_order}\u0022 (route name: \u0022rest.commerce_cart_canonical.GET\u0022)"}

The site is llangollenbrewery.com

I can't find any answers to this online so hoping someone can point me in the right direction as it must be a config error somewhere I'd imagine.

Let me know if you have any questions, any help would be much appreciated so the site can take orders again ASAP.

Thanks